Electrowinning of manganese



, a 2,755,241 mted States Patent Ofice P........ ant-1,1956

ELECTROWINNING F MANGANESE Glen D. Bagley, Lewiston, and Michael C.Carosella, Niagara Falls, N. Y., assignors to Union Carbide and CarbonCorporation, a corporation of New York No Drawing. Application July 28,1952, Serial No. 301,382

4 Claims. (Cl. 204-105) The present invention relates to cathodes foruse in the electrowinning of manganese from aqueous solutions and moreparticularly to a method for the preparation and use of such cathodes.

The characteristics required of successful cathodes for theelectrowinning of manganese, some of which are stated in United StatesPatent No. 2,325,660, are exacting and, heretofore, no metal or metalalloy has been discovered which satisfies all of the characteristics toa sufficient degree.

It is, therefore, the main object of the present invention to provideprocess for the electrowinning of manganese employing cathodes capableof effectively serving for long periods of time Without extensivetreatment and from which deposited metal is easily removed.

Another object is to provide a method for fabricating and conditioningsuch materials to make them suitable for use as cathodes for theelectrowinning of manganese.

Other aims and advantages will be apparent from the followingdescription and appended claims.

It has been discovered that nickel-base alloys containing molybdenum,chromium, iron and Wolfram are very highly resistant to corrosion byaqueous solutions of manganese and ammonium mineral salts, theelectrolyte employed in most commercial processes for the electrowinningof manganese. Additionally, it has been found that such alloys, whenused as cathodes for the electrowinning of manganese, have maintainedtheir polished surfaces for much longer periods of time than washeretofore believed possible of cathodes. These characteris tics,together with the fact that such cathodes permit much easier strippingof the deposited manganese metal serve to make the cathodes of thepresent invention ideal for use in the electrolytic depositing ofmanganese from manganese and ammonium mineral salt solutions.

In accordance with the present invention a nickelbase alloy containing2% to 20% molybdenum, to 25% chromium, 4% to 25% iron, 0.5% to 10%wolfram and to 83.5% nickel is provided in rolled, annealed sheets ofthe desired thickness having smooth surfaces. Thereupon, the sheets aresurface polished with abrasive paper or other suitable equivalent. Theasformed sheet is then degreased prior to its employment as a cathode ina diaphragm cell for the electrowinning of manganese.

It has been found that in many cases metallic manganese can easily bedeposited and stripped from cathodes prepared in accordance with thepresent invention without precoating the cathode surfaces. Inthose caseswhere easier stripping is desired the cathode may be precoated with adilute solution of sodium silicate, or suitable equivalent. It ispreferable to wash and degrease the cathode plates prior to their use inthe electrolytic cell to remove dirt and other contaminants, as well asto improve adherence of the deposited metal to the cathode plates.

Cathodes prepared in accordance with the present invention have beenfound to be far superior to any heretofore employed for theelectrowinning of metallic manganese from aqueous solutions dueespecially to their properties of high resistance to corrosion by theelectrolyte and ease of stripping of deposited metal therefrom. Becauseof the two aforementioned properties the cathodes maintain theirpolished surfaces for longer periods of time, thereby reducing thefrequency of the surface polishing treatment and consequently increasingthe period of use of a given cathode.

Metal alloy cathodes having the two following compositions have beenprepared in accordance with the present invention and have fulfilled therequirements for use in the electrowinning of manganese with greatersuccess than all of the prior art cathodes tested:

Cathode I.15% Cr, 17% Mo, 5% W, 6% Fe, 55% Ni.

Cathode II.22% Cr, 9% Mo, 2% W, 25% Fe, 39% Ni, 0.1% Ta, 0.5% Nb.

For example, surface polished, washed, degreased cathodes having thecomposition given for Cathode 1 above were used in the cathodecompartment of a diaphragm cell for the electrowinning of metallicmanganese in which liters of solution containing 27.2 grams per liter ofmanganese, 128.5 grams per liter of ammonium sulphate, 0.68 gram perliter of sulphur dioxide and some magnesium was continuously introducedas catholyte cell feed. Electrolysis was maintained at a cathode currentdensity of 41 amperes per square foot and high purity manganese metalwas deposited on the cathode. The current efiiciency was 64.8% for adeposition time of 24 hours. The deposited metal was easily removed,leaving a mirror polished surface on the cathode which was used forfurther deposition of manganese metal without further polishing.

It is, of course, to be understood that minor amounts, not in excess of5%, of metals usually found in alloys of this type may be contained inthe alloy. Metals such as tantalum, niobium, vanadium, titanium andaluminum are but a few of the metals normally found in minor amounts insuch alloys.

In addition, metallic and non-metallic impurities of the order ofapproximately 2% may be, and ordinarily are, contained in such alloyswithout substantially altering the composition or properties of suchalloys when used as cathodes for the electrowinning of manganese.

Manganese metal deposited on cathodes in accordance with the presentinvention may be treated to prevent oxidation by dipping the cathodesand deposited metal in a dilute solution of sodium bichromate prior tothe stripping operation.

What is claimed is:

l. A process for the electrowinning of manganese from an aqueoussolution of a manganese and ammonium mineral salt in a diaphragm cellcomprising electrolytically depositing metallic manganese from saidaqueous solution on at least one thin alloy sheet cathode having rolled,annealed, polished, degreased surfaces and containing 10 per cent to 25per cent chromium, 0.5 per cent Wolfram, 4 per cent to 25 per cent iron,2 per cent to 20 per cent molybdenum, and 20 per cent to 83.5 per centnickel; removing said cathode from said cell and removing said depositedmetallic manganese from said cathode; and returning said cathode to saidcell for further deposition of metallic manganese.

2. A process for the electrowinning of manganese from an aqueoussolution of a manganese and ammonium mineral salt in a diaphragm cellcomprising electrolytically depositing metallic manganese from saidaqueous solution on at least one thin alloy sheet cathode having rolled,annealed, polished, degreased surfaces and containing 10 per cent to 25per cent chromium, 0.5 per cent to 10 per cent Wolfram, 4 per cent to 25per cent with a dilute solution of sodium bicl'n'emate to prevent 3. Aprocess for the eiectrowinning of manganese iron an aqueous solution ofa manganese and :nnrnoninn: nineral salt in a diaphragm cell comprisingelectrolytically depositing metallic manganese from said non-conssolution on at least one thin alley sheet cathode having rolled,annealed, polished, degreased surfaces and composed oi: approximately 15per cent chromium, 5 per cent wolfram, 6 per eent iron, 17 per centmolybdenum and 55 per cent nickel; removing said cathode from said celland treating said deposited metallic manganese with a dilute solution ofsodium bichromate to prevent o/."lation thereof; removing said depositedmetallic inang nese from said cathode; and returning said cathode tosaid cell for further deposition of metallic manganese.

4. A process for the electrowinning of manganese from an aqueoussolution of a manganese and ammonium mineral salt in a diaphragm cellcomprising electrolytically depositing metallic manganese from saidaqueous solu' tion on at least one thin alloy sheet cathode beingrolled, annealed, polished, degreased surfaces and composed ofapproximately 22 per cent chromium, 2 per cent Wolfram, 25 per centiron, 9 per cent molybdenum, 39 per cent nickel, 0.1 per cent tantalum,and 0.5 per cent niobium; removing said cathode from said cell andtreating said deposited metallic manganese with a dilute solution ofsodium bichromate to prevent oxidation thereof; T011101 ing saiddeposited metallic manganese from said cathode; and returning saidcathode to said cell [or further deposition of metallic manganese.

References Cited in the file of this patent UNITED STATES PATENTSChamberlain Aug. 3, 1943 Jacobs Jan. 24, 1950 OTHER REFERENCES

1. A PROCESS FOR THE ELECTROWINNING OF MANGANESE FROM AN AQUEOUSSOLUTION OF A MANGANESE AND AMMONIUM MINERAL SALT IN A DIAPHRAGM CELLCOMPRISING ELECTROLYTICALLY DEPOSITING METALLIC MANGANESE FROM SAIDAQUEOUS SOLUTION ON AT LEAST ONE THIN ALLOY SHEET CATHODE HAVING ROLLED,ANNEALED, POLISHED, DEGREASED SURFACES AND CONTAINING 10 PER CENT TO 25PER CENT CHROMINUM, 0.5 PER CENT WOLFRAM, 4 PER CENT TO 25 PER CENTIRON, 2 PER CENT TO 20 PER CENT MOLYBDENUM, AND 20 PER CENT TO 83.5 PERCENT NICKEL; REMOVING SAID CATHODE FROM SAID CELL AND REMOVING SAIDDEPOSITED METALLIC MANGANESE FROM SAID CATHODE; AND RETURNING SAIDCATHODE TO SAID CELL FOR FURTHER DEPOSITION OF METALLIC MANGANESE.